Electrode element for corona treater

ABSTRACT

A corona treater includes an active electrode which has one or more insulated electrode elements slidably supported by an insulating track. A contact spring connects each electrode element to a conductive electrode bar embedded in the track, and sheet material to be treated is fed through a treatment zone created between an active discharge surface on each electrode element and a bare metal roller electrode.

This is a division of application Ser. No. 569,264, filed Jan. 9, 1984,now U.S. Pat. No. 4,533,523.

BACKGROUND OF THE INVENTION

The field of the invention is corona treater stations, and particularly,the construction of electrodes for such stations.

Corona treater stations for sheets, or webs of plastic materials takemany forms. Typically, the material to be treated is fed through atreatment zone in which one surface of the material is bombarded withions produced by a high voltage alternating electric field. The materialis supported in the treatment zone by a conductive roller which alsoserves as one electrode for the treater. A second, active electrode issupported in the treatment zone and is spaced from the conductive rollerequidistantly along its length. For many years the active electrode hastaken the form of metal segments which are pivotally attached to a bar,or beam, and which can be selectively swung away from the roller toremove them from the treatment zone. In this manner, the width of thetreatment zone can be adjusted to accommodate webs of different widths.

One difficulty with segmented electrodes is that they produce an uneventreatment. This may be caused either by an uneven spacing of thesegments from the roller electrode or by changes in the electric fieldstrength at the junction of adjacent segments.

Treater station reliability has been significantly increased recently byemploying an elongated active electrode having a coating, or jacket,made of a heat resistant insulating material. Such a structure isdisclosed in co-pending U.S. patent application Ser. No. 237,964 filedon Feb. 25, 1981, where the active electrode is constructed from ahollow quartz rod which is filled with a conductive material and whichextends the entire length of the roller electrode. While suchconstructions provide very uniform treatment and do not require aninsulating layer on the roller electrode, they are difficult tomanufacture. It is difficult to form long tubes of quartz of ceramicmaterials and it is difficult to fill them with conductive material.Also, the differences in the thermal coefficients of expansion of theinsulating rod and its supporting structure make it difficult to mountthe rods.

A number of attempts have been made recently to provide a segmentedactive electrode in which each segment is covered with an insulatingjacket. Characteristically, such structures have employed a metal bar orbeam which extends along the length of the roller electrode and whichsupports a series of metal fingers that each extend from the beam towardthe roller electrode. In this respect they are very similar to the wellknown segmented metal electrodes in that the separate metal fingers canbe removed or swung away to adjust the width of the treatment zone. Thedifference is that a jacket of insulating material is slipped over theend of each metal finger to allow bare roll treating. The uneventreatment produced by segmented active electrodes is greatly amplifiedwhen the segments are insulated in this manner, and such constructionshave not thus far been commercially successful.

SUMMARY OF THE INVENTION

The present invention relates to an insulated active electrode for atreater station which may be segmented for ease of manufacture and foraltering the width of the treatment zone. The invention includes a trackwhich is made of an insulating material and which extends along thelength of a roller electrode and is spaced equidistantly therefrom, aninsulated electrode which is slidably supported by the track, aconductive electrode bar which extends along the length of the track,and a brush contact connected to the insulated electrode and extendingoutward therefrom into sliding engagement with the electrode bar.

A general object of the invention is to provide an insulated electrodewhich is easy to manufacture. Rather than constructing a singleinsulated electrode of great length, a plurality of shorter electrodesmay be constructed and slidably mounted side-by-side on the track toprovide the desired treatment width. The electrodes may be provided in avariety of lengths and a plurality of brush contacts may be providedalong the length of large electrodes.

Another general object of the invention is to provide an insulatedelectrode which is easy to mount. The insulated electrode slides ontothe track where it is firmly supported. No fasteners or bonding agentsare required.

Another object of the invention is to provide an electrode in which thespacing from the roller electrode is precisely determined along itslength. The track may easily be aligned for equal spacing from theroller electrode and the individual electrodes mounted to the track canbe identically molded. The proper number of electrodes can be placed onthe track and slid into position in the treatment zone. No fasteners oradjustments are required when electrodes are added or replaced, thusmaking it a simple and inexpensive task to adjust the width of thetreatment zone or replace defective electrodes.

Another object of the invention is to reduce the heat produced insidethe electrode. The electrode includes a case made of a heat resistant,electrically insulating material such as quartz or ceramic. This case isshaped to slidably engage the track and retain the electrode in itsproper position. A metal plate is contained within the case and ispositioned tightly against the inner surface of a bottom wall of thecase. The brush contact connects to the plate, but it provides nosupport function which might dislodge the plate from its tightengagement with the bottom wall. Indeed, the brush contact may beconstructed to provide a bias force which promotes tighter engagement ofthe plate and the bottom wall of the case. This tight engagement ensuresthat no heat producing ionization occurs inside the electrode.

Yet another object of the invention is to insulate the electrode barfrom its surroundings. The electrode bar may be disposed in a slotformed along the length of the track. The electrode bar is thussurrounded on three sides by the insulating material from which thetrack is made and the exposed surface is covered by the electrode. Ifelectrodes are removed to narrow the treatment zone, the resultingexposed portion of the electrode bar can be covered with an inoperable,insulating segment which slides onto the track.

Still another object of the invention is to provide uniform treatmentacross the width of the treatment zone. Each electrode is shaped toprovide an active discharge surface which is directed toward the rollerelectrode. The discharge surface is bounded on two opposing sides by endwalls which mate with the end walls of adjacent electrodes. These endwalls are oriented at an angle with respect to the direction of travelof the material being treated and there is thus no untreated gap at theintersection of the discharge surfaces on adjacent electrodes.

The foregoing and other objects and advantages of the invention willappear from the following description. In the description, reference ismade to the accompanying drawings which form a part hereof, and in whichthere is shown by way of illustration a preferred embodiment of theinvention. Such embodiment does not necessarily represent the full scopeof the invention, however, and reference is made therefore to the claimsherein for interpreting the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front elevation view with parts cut away of the treaterstation of the present invention;

FIG. 2 is a view in cross section taken along the plane 2--2 indicatedin FIG. 1;

FIG. 3 is a partial bottom view of the active electrode which forms partof the treater station of FIG. 1 and which shows the intersection of twoadjacent electrodes;

FIG. 4A is a view in cross section through a short electrode taken alongthe plane 4--4 indicated in FIG. 3;

FIG. 4B is a view in cross section through an alternative electrodeconstruction taken along a plane perpendicular to the plane 4--4indicated in FIG. 3; and

FIG. 5 is a partial perspective view of the track which forms part ofthe treater of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring particularly to FIG. 1, the treater station is constructedwith steel framework 1 which includes a pair of spaced upright sideassemblies 2 and 3 supported by a base 4. A circular cylindrical metalroller 5 is supported between the side assemblies 2 and 3 and a web ofmaterial to be treated (not shown in the drawings) is fed over theroller 5 causing it to rotate. The roller 5 also connects to oneterminal of a high voltage power supply (not shown in the drawings) andit serves as one electrode for the treater station.

Referring particularly to FIGS. 1 and 2, also supported by the framework1 is a header 6 which extends between the side assemblies 2 and 3 and isaligned parallel to the roller electrode 5. The header 6 is formed froman aluminum tube which is rotatably mounted to the side assemblies 2 and3. A pair of extruded aluminum skirts 7 and 8 are fastened to the header6, and these are spaced apart to form a passageway, or pipe 10 whichextends from the header 6 to the surface of the roller electrode 5.Openings 11 are formed along the length of the header 6 between theskirts 7 and 8, and cooling air flows through these openings from a gap12 formed between the skirt 7 and the roller electrode 5. As shown bestin FIG. 1, this cooling air flows from the openings 11 to one end of theheader 6 where it is drawn through the side assembly 3 and into anexhaust vent 13.

As shown best in FIG. 2, an active electrode 15 is disposed inside thepipe 10 adjacent the surface of the roller electrode 5. The activeelectrode 15 is supported by a track member 16 which extends the fulllength of the skirts 7 and 8 and which is constructed from anelectrically insulating material. The orientation of the track 16 isprecisely adjusted to ensure that it is spaced equidistantly from thesurface of the roller electrode 5 at all points along its length.

Referring particularly to FIGS. 2 and 5, the track 16 includes a pair ofspaced rails 20 and 21 which are connected together by a series of crossmembers 22. The rails are parallel to each other and they are notched ontheir inner surfaces at 23 and 24 along their entire length. A channelmember 25 is fastened to the cross members 22 and is centered betweenthe rails 20 and 21 along their entire length. The entire structure isfastened between the skirts 7 and 8 by bolts 19 which extend througheach cross member 22.

The active electrode 15 which is supported by the track 16 is comprisedof an electrode bar 30 and one or more electrode elements 31. Theelectrode bar 30 is made of a highly conductive metal and it is disposedin a recess formed on the bottom surface of the channel member 25. Oneend of the electrode bar 30 is connected to the high voltage powersupply which operates the treater station, and the electrode bar 30extends along the entire length of the track 16.

The electrode elements 31 are slidably connected to the track 16 andthey are disposed side by side along its length. Each electrode element31 presents a flat discharge surface 32 which is directed towards thesurface of the roller electrode 5. The electrode element 31 is retainedto the track 16 by a pair of spaced support walls 33 which are shaped toslidably engage the rails 20 and 21. A rib 34 is formed along the upperedge of each support wall 33, and this rib 34 rides in one of thenotches 23 or 24 to hold the electrode element 31 in place.

Referring particularly to FIGS. 2 and 5, the track 16 is constructed toprovide cooling air to the active electrode 15. A series of openings 51are formed along the length of the rail 20 and a corresponding set ofopenings 52 are formed along the length of the rail 21. The cooling airwhich enters through the gap 12 follows the paths indicated by thearrows in FIG. 2, with a portion of it flowing over the dischargesurface 32 of the electrode element 31 and a portion of it flowingthrough its interior. To enhance the air flow over the active dischargesurface 32, a barrier 53 is fastened to the skirt 8 by bolts 54. Thebarrier 53 extends the entire length of the roller electrode 5 and thespacing between a lip 55 formed along the lower edge of the barrier 53and the roller electrode 5 may be adjusted to allow passage of the web,but limit the entry of air. Openings 11a formed in the header 6 betweenthe skirt 8 and the barrier 53 further enhance the cooling air flowpattern as shown.

Referring particularly to FIGS. 3 and 4, the electrode elements 31 maybe constructed in a variety of lengths. For example, a very longelectrode element 31 may be used on a corona treater station and aseries of short electrode elements 31 may be used at either end. Thewidth of the treatment zone can then be easily adjusted by removing oradding short electrode elements 31 as required. Two separateconstructions of the electrode element 31 are described herein. Thefirst construction is shown in FIG. 4A as applied to a short electrodeelement 31 and the second construction is shown in FIG. 4B.

Referring particularly to FIG. 4A, the first electrode elementconstruction includes a case 35 made of a heat resistant, electricallyinsulating material. A ceramic material is preferred, although a glassor quartz material may also be employed for this purpose. A conductivemetallic coating 36 is deposited inside the case 35 of its bottom and athin layer 37 of powdered aluminum is laid down over this coating 36. Ametal plate 38 which is shaped to follow the contours of the case 35 isinserted over the conductive layer 37, and an arcuate metal contactspring 39 is welded to the top surface of the plate 38 at its center.The metal plate 38 is retained in position by a silicon rubber adhesive40.

Referring particularly to FIG. 4B, the second preferred construction ofthe electrode element also includes a case 35 made of a heat resistant,electrically insulating material. A conductive metallic coating 36 isdeposited on the inside of the bottom of the case 35 and a metallicplate 38 rests against this coating 36. Welded to the plate is a metalsleeve 60 which extends upward therefrom to the brim of the case 35. Acoiled contact spring 39B is disposed in the sleeve 60 with its lowerend engaging the metal layer 36 and its upper end engaging the electrodebar 30. The contact spring 39B is under compression to provide a biasforce which insures good electrical connections at each of its ends. Aset of sleeves 60 and contact springs 39B may be employed along thelength of large electrode elements 31 to insure even distribution ofcurrent along the discharge surface 32 with minimal resistive heating.

Referring again to FIGS. 2 and 3, when the finished electrode elements31 are placed in position on the track 16, their contact springs 39 or39B are compressed against the surface of the electrode bar 30. Theforce which results from this compression serves to enhance electricalcontact between the electrode bar 30, the contact spring 39 or 39B, themetal plate 38, and the bottom wall of the case 35. When high voltage isapplied to the bar electrode 30, the electric field is concentrated inthe gap between the discharge surface 32 and the roller electrode 5. Thecorona which is produced in this treatment zone bombards the surface ofweb materials which are fed over the roller electrode 5. Heat generatedduring this treatment process is carried away by the cooling air whichis circulated over the active discharge surface 32.

As shown best in FIG. 3, the electrode elements 31 are shaped to insureuniform treatment across their junction with an adjacent electrodeelement 31. The path of the web material as it is fed through thetreatment zone is indicated by arrow 45. The end walls 46 of eachelectrode element 31 are aligned at an angle with respect to this feedpath 45 and are shaped to mate closely with the end wall 46 of anadjacent electrode element 31. In the preferred embodiment the end walls46 are planar and they are aligned at an angle of thirty degrees to thefeed path. As a result, there is a region at the intersection of twoadjacent electrode elements 31 where treatment is slightly reduced, butthere is no abrupt or drastic change in treatment level across theentire width of the material.

In some applications it may be desired to provide regions which areuntreated. This can easily be accommodated by removing the electrodeelements 31 at the appropriate points across the width of the web. Inthe alternative, inactive elements which do not connect to the barelectrode 30 may be placed at the points where treatment is notrequired. An inactive element may be constructed by removing the contactspring 39 and metal plate 38 from an active electrode element 31. Suchinactive elements cover the bar electrode 30 to provide an insulatingbarrier which prevents undesired arcing.

I claim:
 1. An electrode element for a corona treater, which comprises;acase made from a heat resistant electrically insulating material andhaving a bottom wall which provides a discharge surface and a pair ofspaced side walls which connect to the bottom wall and extend upwardtherefrom; a metal plate disposed between the side walls and against thebottom wall of the case on the side opposite the discharge surface;means for connecting the case to the corona treater; and a contactspring which is disposed between the side walls of the case and havingone end in electrical contact with the metal plate and its other endextending upward to make electrical contact with an electrode bar on thecorona treater.
 2. The electrode element as recited in claim 1 in whichthe means for connecting the case to the corona treater includes a ribformed on each side wall which is shaped to slidably engage a track onthe corona treater.
 3. The electrode element as recited in claim 1 inwhich a sleeve connects to the metal plate and the contact spring is acoiled spring which is disposed in the sleeve.
 4. The electrode asreceited in claim 1 in which the case includes a pair of spaced endwalls which connect to the bottom wall and extend upward therefrom. 5.The electrode as recited in claim 4 in which the bottom wall has theshape of a parallelogram.